Over-center snap switch



Sept. 27, 1966 P. D. GROVER 3,275,773

OVER-CENTER SNAP SWITCH Filed April 9, 1964 2 $heets$heet 1 @ZVENTOR.

BY l ng/zen, WW %t, 777%? Sept. 27, 1966 P. D. GROVER 3,275,773

OVERCENTER SNAP SWIITCH Filed April 9, 1964 2 SheetsSheet 2 UnitedStates Patent 3,275,773 OVER-CENTER SNAP SWITCH Philip D. Grover, TwoRivers, Wis., assignor to Grover Products Corporation, a corporation ofIllinois Filed Apr. 9, 1964, Ser. No. 358,570 4 Claims. (Cl. 200-138)This invention relates to over-center snap structure and, moreparticularly, to a device responsive to conditions such as temperatureor humidity for effecting a snap action which is usefully employed as ameans of switching an electrical circuit, as a circuit breaker forinterrupting an electrical circuit, or for obtaining useful mechanicalmotion for opening valves and the like.

An object of this invention is to provide an over-center snap structurehaving a new and improved construction for more economical manufactureand more positive action.

Another object of this invention is to provide a condition-responsive,snap-action member which is simple and economical to manufacture.

Another object of this invention is to provide a thermally responsivesnap switch in which the required snap action is developed essentiallyfrom a single annular stressed piece of bimetal for positive switchingat a predetermined temperature.

Still another object of this invention is to provide a thermallyresponsive switching device as defined in the preceding paragraph withan unstressed compensating member which will maintain pressure on theelectrical contacts thereof, right up to the point of snap, to effect apositive clean-cut switching action with no uncertain electricalcontinuity and changes of resistance which has been characteristic ofmost bimetallic thermostatic devices.

A further object of this invention is to provide a thermally sensitivepre-set temperature snapping switch which can have mechanical stressesmanufactured therein overridden by .an adjusting means so that thethermal switch will operate at temperatures required in varyingapplications.

A further object of the invention is to provide a condition-responsiveactuator in which the actuator is formed as an annular member which ismechanically stressed to one concave configuration and with the memberhaving condition-responsive material on the concave side thereof whichexpands at a greater rate than the remainder of the annular body to snapthe body from one concave to oppositely concave configuration.

Another object of the invention is to provide an overcenter snapstructure having an annular body with mechanical stresses therein withthe body being supported at a fulcrum point adjacent one part of theperiphery of the body and actuating means engaging the body adjacent theother periphery with the fulcrum point and actuating means lyinggenerally on a line which is a radian of the body to provide minimumtwisting actuation of the structure.

A further object of the invention is to provide a simply andeconomically manufactured circuit breaking device utilizing an annularstressed bimetal member which can respond to an electrical overload byopening the circuit in which it is a component and which can eitherautomatically restore the circuit after the overload condition isremoved or the circuit can remain open until manually or mechanicallyreset.

Further objects and advantages will become apparent from the followingdetailed description taken in connection with the accompanying drawingsin which:

FIG. 1 is a perspective view of an annular upwardly concave structure ofbimetal with the high expansive material on top;

Patented Sept. 27, 1966 "ice FIG. 2 is a perspective view of thestructure shown in FIG. I mounted on a supporting structure and carryingan electrical contact together with the final positiontemperature-induced movement shown in broken line;

FIG. 3 is a perspective view of a preferred embodiment of the basicelement with an unstressed compensating member projecting into thecentrally disposed opening of the body;

FIG. 3A is a perspective view of a planar periphery mounted thermal snapelement with a radially outward extending unstressed leg portion,serving here as an actuating member, and a radially inward extendingmember acting as a work take-off contact carrying member;

FIG. 4 is a vertical central section of the structure shown in FIG. 3shown mounted illustrating how the compensating member tips thestructure to offset the flatten-ing effect of a temperature rise, or thelike, on the position of the actuating part which would otherwise tendto be displaced downwardly;

FIG. 5 is a perspective view of an embodiment of the preferred thermalelement in a snap switch structure with associated fixed electricalcontacts;

FIG. 6 is a perspective view of an embodiment of the preferred thermalelement in a snap switch structure adapted to change the requirementsfor causing actuation of the snap switch;

FIG. 7 is a perspective sectional view of an embodiment of the preferredthermal element in a circuit breaking structure, such as a typicalhousehold fuse, which will automatically reset itself;

FIG. 8 is a perspective exploded view of an embodiment of the preferredthermal element in a circuit break ing application, as a typicalhousehold fuse, containing a spring-loaded reset button to restore thecircuit; and

FIG. 9 is a perspective view of another embodiment showing the minimalrelation of fulcrum point and actuating means for the snap structure.

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail an embodiment of the invention together with modificationsthereof with the understanding that the present disclosure is to beconsidered as tn exemplification of the principles of the invention andis not intended to limit the invention to the embodiments illustrated.The scope of the invention will be pointed out in the appended claims.

The basic annular stressed disc is shown in FIG. 1. This disc isidentified at 10. This disc is constructed of two layers of material,with one layer 12 being conditionresponsive material and the other layer13 being spring metal. The condition to which the material 12 isresponsive can either be heat or humidity. In order to beheat-responsive, the body would basically consist of bimetal and forhumidity response, the layer 12 would be of a hygroscopic material, suchas nylon, bonded to the layer 13. It is apparent that, since bimetal isa laminate of two metals with different rates of expansion, theapplication of heat will cause the higher rate of expansion metal 12 toexpand more in all directions than the low expansion metal 13. Thismanifests itself well in an annular unstressed disc which expands froman essentially planar structure at ambient temperature to a form thatmay be considered as embracing a portion of a sphere. While the morefamiliar form of a strip of bimetal bends along its axis, it is oftenoverlooked that bending takes place in all directions.

As taught in my prior patent No. 2,861,143, planar spring material may"be stressed out of its planar form by shortening a portion of itsperiphery with a Wave or corrugation, so that the material may beconsidered to lie on a spherical surface.

The stresses which are introduced by mechanical deformation of thestructure are mechanical stresses, and those stresses which temporarilydeform or bend the bimetal may be called thermal stresses. In the finalanalysis at any given moment in the movement of the device, the stressesare essentially of the same quality. The difference is that themechanical stresses do not vary with a condition, such as heat, whilethe thermal stresses are a function of the temperature of the device.

The annular disc as shown in FIG. 1 has been mechanically stressed byshortening a portion of its periphery, as by a corrugation 11. Thisdeformation results in an upwardly concave structure with the highexpansive material 12 on the upper side of the disc. This spring metallayer 13 is on the lower side of the disc. The application of heat tothe structure will result in thermal bending forces radially acting toovercome the mechanically-induced stresses. At a certain point in thetemperature rise, the thermal stresses will overcome the mechanicalstresses and cause the member to snap inside-out. Similarly, the sameaction would occur in a humidity-responsive construction.

With a decrease in temperature from the upper temperature reached, thethermal stresses causing the bimetal to bend are lessened and finallyreach the point where the mechanical stresses in the spring-like discmember overcome the diminishing thermal stresses and the device returnsto its original position with a snap action.

When the disc 10 is first stressed mechanically out of its essentiallyplanar form, a bias may be introduced, as by permanently bending theperiphery of the body, to accentuate or diminish the mechanical stressesholding the disc in a concave form. This bias may be of such magnitudethat, once forced over center, the disc will not return to its originalposition. Or again, the bias may be such that it takes very littlepressure to snap the disc -over center.

In the preferred practice, the biasing is achieved by bending the metalon one side of the corrugation to a greater or lesser angle relative tothat-on the other side.

The amount of mechanical stressing of the annular disc is a function ofthe amount of foreshortening which in turn is a function of the amountof material drawn into the corrugation 11.

In FIGURE 2, the basic disc 10 is mounted at one portion of itsperiphery on a mounting 14 and has an electrical contact 15 at anotherportion of its periphery. This structure may be considered as a thermalfunctioning element of an electric snap switch when suitable fixedcontacts are positioned to engage the electrical contact on the disc.

For best use as an electrical switch, it is necessary to have themovable contact in pressurized engagement with the fixed contact topermit the current to flow through the junction effected. The action ofthe disc 10 is improved by use of a bimetallic compensating member whichis essentially unstressed mechanically. This structure is shown in FIG.3 in which an annular disc 20, similar to disc 10, with a corrugation 21has an unstressed compensating member 22. With the structure mounted ona post 23 by the compensating member, as shown in FIG. 4, thecompensating member can bend in a direction to tilt the whole structureas it tends to flatten out with the application of heat. The movablecontact 24 remains in pressurized contact with a fixed contact.

Suflicient length of stock to form the compensating member can beobtained from within the opening of the annular disc. The same effectcould be obtained with a separate bimetallic support outside of theannular disc or the supporting portion could be blanked from the samepiece of material. A separate compensating member used as a mountingmeans may be utilized in a configuration where it extends radiallyoutwards from the stressed mem ber providing the high expansive side ofthis compensating bimetal member is opposite the high expansive side ofthe stressed member so that it will tilt the stressed member to offsetthe flattening effect of the stressed member, as a change in environmentcauses the stressed ele ment to approach the snap point. Thus, anelectrical contact diametrically across the stressed member from thesupport point can maintain or even increase its pressure on the fixedcontact prior to snap.

This unstressed member 22 can be used as a mounting and thuscompensates, as shown in FIG. 4, or can be used as an actuating means ora mechanical power takeoff. When used as a mounting, the compensatingmember does not interfere with the action of the stressed disc. If theunstressed member extends radially to the outside it provides a largedisplacement relative to the displacement of the periphery of the disc20. This extension can be used as a work take-off member, or as anactuating member. It then would not serve as a compensating mountingmeans, as in keeping a movable contact in pressurized conjunction with afixed contact to offset the flattening effect of the concave disc priorto snap, but would enhance this lift-off effect. When the member 22 isused as an actuating means, a downward actuating force will snap thestructure up or down depending on whether the compensating member ispositioned inside or outside the disc. As a mechanical take-off, theintegral unstressed member can provide a larger displacement whenextending from the exterior of the disc than if within the interior ofthe disc, as it is limited by the length of the opening in thestructure.

FIG. 3A shows a peripherally hinged snap unit 25 similar to disc 20 witha radially extending internal unstressed member 26 and a radiallyoutward extending member 27, either of which can be used as an actuatingmember to twist the periphery and effect a snap, or as a Work take-offmember as to snap a movable contact to engage a fixed contact. In thisexample there is no compensating function. A plurality of posts 28 withnotches 29 support the disc at its periphery.

A complete switch utilizing the structure of FIG. 4 is shown in FIG. 5.As shown in FIG. 5, a stressed annular disc 30 of bimetal constructedsimilarly to disc 20 shown in FIG. 4 has an unstressed compensatingmember 31 by which the disc is mounted to a mounting post 32 and a base33a of dielectric material. A central common terminal 33 has a pair offlexible leaves 34 and 35, each of which carry a contact 36 and 37,respectively. A leaf 38, carrying a contact 39, forms, with the contact36, a normally closed circuit.

When the temperature reaches a suflicient level to have the thermalstresses overcome the mechanical stresses, the disc 30 snaps to anoppositely concave configuration to release the engagement betweencontacts 36 and 39 and cause a contact 37 on the leaf 35 to engage acontact 41 on a leaf 42 of the normally open side of the circuit. Eachof the leaves 38 and 42 are secured to an insulating mounting by meansof rivets, such as indicated at 43, and each of the leaves has aterminal screw, as indicated at 44 for the lea-f 38. This switch cansense the surrounding air temperature and respond with a snap action toswitch an electrical circuit at a predetermined temperature. Also, theswitch can be used to sense the temperature of an object, such as acontainer being heated, by having a thermally-conductive path throughthe base 33a to the disc 30. The thermal conductivity of a base whenformed of metal is superior to that of air, so as to increase thesensitivity of the unit. In such instances where electrical shock wouldbe a hazard, the disc 30 can be removed from the circuit and solely usedas an actuator to move the necessary contacts, as through an insulatingactuating member, 40.

FIG. 6 shows another embodiment of switch in which it is possible tochange the temperature at which the unit will snap. As statedpreviously, the bimetal responds to heat to exert stresses which canovercome the mechanical stresses to shift the disc of material to anopposite concave configuration. If the mechanical forces to be overcomeare increased, it will require more of a temperature change toaccomplish this. Conversely, if the mechanical forces are lessened, alesser change in temperature will be required. In the switch shown inFIG. 6, a disc 50, similar to disc 30 shown in FIG. 5, is mounted by acompensating member 51 on a heat conductive, metal mounting post 52having a base 53 which can provide a high conductive path for heat. Aseries of three leaves 54, 55 and 56 are mounted on the base 53 by aninsulating mounting block 57 and each has an electrical terminal 58, 59,and 60, respectively. An insulating button, 70 on disc 50 may be used tokeep the members 50, 51, 52 and 53 electrically isolated from theswitching elements where metal is used as a high heat transmissionmaterial in the disc supporting elements. The leaves 54 and 55 aresprung to move downwardly toward the base 53 and the actual position ofleaf 54 is determined by a threaded shaft 61 having a manually-operableknob 62 and engageable with an insulating pad 63 on the base 53. Thisthreaded shaft is threaded into the upper leaf 54 whereby the positionof the lea-f 54 from the base 53 can be determined by the rotativeposition of the shaft. Leaf 55 is biased down so that contact 67 willengage contact 68, when the pressure exerted by disc 50 is released bysnapping over center.

With the disc 50 in its concave configuration, as shown in FIG. 6, thecontacts 65 and 66 on the leaves 54 and 55 are in contact as maintainedby the disc 50. With an increase in temperature, the disc 50 snaps overcenter and the contact 67 on leaf 55 moves into engagement with thecontact 68 on the leaf 56 by virtue of the downward bias of leaf 55.This structure illustrates the primary principle in modifying the totalmechanical forces involved in the switch. The leaf 54 through theadjustment shaft 61 determines the upper position of the annular disc 50so that this disc may not move upwardly to its final position and thusless thermal stresses to overcome the mechanical stresses are requiredto snap the structure over center. It is thus possible to vary thetemperature at which the switch will respond.

Another use of the annular stressed disc of bimetal is shown in FIG. 7in a circuit breaking application, such as a household fuse. With theconventional threaded body 70, a conducting portion 71 has a conductingpost 72 to which a compensating member 73 is attached and mounts theannular disc 74 similar to disc 20. The disc 74 carries a contact 75engageable with a contact 76 associated with the conductive casing ofthe fuse 77. As shown in FIG. 7, the annular disc 74 is in an upwardlyconcave configuration, with the high expansion material on the undersidewith the fuse open. In this instance, the disc 74 is formed of materialand proportioned so that the resistance of the unit when encountering anelectrical overload will cause it to be heated by its own resistanceuntil suflicient thermal stresses are built up to effect an overcomingof the mechanical stresses and the unit snaps over center to theposition shown. In normal usage, the disc 74 would be in its downwardlyconcave configuration, with the contacts 75 and 76 in engagement. Inthis embodiment, the unit is self-restoring. Once the disc 74 cools, thecircuit would be reestablished and would be maintained closed so long asthere is no electrical overloading. In practice, an electricalresistance element such as nichrome wire may be located in closeproximity to the thermal snap element, (73 and 74), and connectedelectrically in series with the thermal snap element to augment theheating effect of current flowing through the resistance of the bimetalfrom which the disc is made. This additional heat would improve theresponse time and the sensitivity of the device.

In the embodiment of FIG. 8, which is also a circuit breakingapplication such as a household fuse, the structure is generally thesame as that shown in FIG. 7 in which a disc 80 is mounted on aconductive post 81 by a compensating member 82 with the disc carrying acontact 83 engageable with a contact 84 associated With a conductiveexterior of the fuse. The parts being shown in FIG. 8 open after anoverload. In this embodiment, bias has been placed in the disc so thatthe disc 30 will remain in its snapped-over configuration even aftercooling. In order to reset the fuse, it is necessary to mechanicallyshift the disc 80 to a downwardly concave configuration as accomplishedby depression of a plate 87 fitting under an enclosing cover 88 having aplunger 89 extending through an opening 90. The plunger 89 can bemanually depressed against a spring 91 to have a lug 92 engage a raisedportion 86 of the disc and snap it, by prying against a downturnedportion of the disc which acts as a fulcrum, thus twisting a portion ofthe periphery of the disc to effect a resetting snap switch action.

In FIG. 9, an annular disc 100, with compensating member 101 formed ofstressed bimetal similar to those previously described, is disclosed inWhich the disc can be mounted on a post 102. In this embodiment, afulcrum 103 on a supporting structure is provided in contact with thedisc closely adjacent the inner periphery thereof and a movableactuating member 104 is provided adjacent the outer periphery of thedisc. A line extending between the fulcrum 103 and the actuating member104 where it engages the disc lies generally along a radian of theannular member. This is a construction in which the basic action inobtaining a snap of the annular member is accomplished by applying aminimum actuating displacement between the fulcrum point and the pointof actuating force. This structure utilizes a minimum actuating movementdifferential.

As will be seen from the foregoing description, the basic shape of thebimetal disc is that of an annulus which inherently, upon a change orincrease in temperature from the ambient temperature, will assume ashape to embrace a spherical segment. This approximate same shape isalso induced by the shortening corrugation, as formed in the disc. Theincrease in temperature exerting the thermal stresses causes lines ofradial force to impart a twisting action to the periphery or body of thedisc to overcome the mechanical stresses. This follows the naturalaction of the bimetal disc and achieves the desired snap action mostefficiently. If the configuration were other than annular, such astriangular or rectangularly elongate, the bending forces induced by agiven temperature rise attempt to make the piece move to embrace aspherical configuration which is not that which the part is shaped totake, so that a substantial portion of the forces would be usedinetfectively.

I claim:

1. A thermal responsive snap switch comprising, a heat conducting base,an annular body of bimetal, a wave in said body inducing an initialstress and concave configuration therein, an unstressed compensatingmember extending inwardly from the periphery of the body defining amounting for said annular body, a heat conducting member extending fromthe base on which the compensating member is mounted, a stationarycontact and a movable contact, heating of the body causing overcentermovement of the body to change the relation of said contacts, a leafcarrying said movable contact and engageable by said annular body.-

2. A snap switch as defined in claim 1 and having means for adjustablylimiting the movement in one direction of said leaf and correspondinglylimiting the movement of the annular body in the same direction.

3. A snap switch structure responsive to ambient conditions comprising abase for mounting of the switch components, a fixed switch contactsupported by said base, a movable switch contact selectively engageablewith the fixed contact, and means carrying said movable contactincluding an annular body formed of spring metal with an interioropening and said body having a wave at one location along the lengththereof to introduce mechanical stress into the body and place said bodyin a concave configuration, an integral unstressed compensating legextending inwardly into said opening, fastener means adjacent the end ofsaid leg attaching the leg to said base with the contacts in engagementand a layer of hygroscope material on the concave side of the body andthe same side of said leg whereby a change of condition acts to bend theleg to maintain the contacts in engagement until the change is of amagnitude to create a force overcoming the mechanical stress in saidbody and shift said body over-center to disengage said contacts.

4. A condition responsive snap switch comprising a base, an annular bodyof condition responsive material, a wave in said body inducing aninitial stress and concave configuration therein, an unstressedcompensating member extending inwardly from the periphery of the bodydefining a mounting to the base for the body adjacent a free end of saidmember, a stationary contact and a movable contact, a leaf membercarrying said movable contact and extending to a position for selectiveengageengagement by said body whereby the body in snapping over-centershifts the leaf member to change the relation of the contacts, andadjustable means directly in line 8 with said leaf member contact and inback-up engagement therewith for limiting the movement in one directionof said leaf member and correspondingly limiting the movement of theannular body in the same direction.

References Cited by the Examiner UNITED STATES PATENTS 1,988,345 1/1935Vaughn 200-1l3 2,509,593 5/1950 Goddard ZOO-61.06 2,828,385 3/1958Malone 200113 2,828,386 3/1958 Malone 200-113 2,834,853 5/1958 Hood200-1 13 2,856,487 10/1958 Mang 200113 X 2,863,024 12/1958 Romine200-138 2,951,137 8/1960 Epstein 200113- 2,954,445 9/ 1960 HargreavesZOO-61.06 3,110,788 11/1963 Welsh 200113 BERNARD A. GILHEANY, PrimaryExaminer.

ROBERT K. SCHAEFER, Examiner.

L. A. WRIGHT, T. D. MACBLAIN, Assistant Examiners.

1. A THERMAL RESPONSIVE SNAP SWITCH COMPRISING, A HEAT CONDUCTING BASE,AN ANNULAR BODY OF BIMETAL, A WAVE IN SAID BODY INDUCING AN INITIALSTRESS AND CONCAVE CONFIGURATION THEREIN, AN UNSTRESSED COMPENSATINGMEMBER EXTENDING INWARDLY FROM THE PERIPHERY OF THE BODY DEFINING AMOUNTING FOR SAID ANNULAR BODY, A HEAT CONDUCTING MEMBER EXTENDING FROMTHE BASE ON WHICH THE COMPENSATING MEMBER IS MOUNTED, A STATIONARYCONTACT AND A MOVABLE CONTACT, HEATING OF THE BODY CAUSING OVERCENTERMOVEMENT OF THE BODY TO CHANGE THE RELATION OF SAID CONTCTS, A LEAFCARRYING SAID MOVABLE CONTACT AND ENGAGEABLE BY SAID ANNULAR BODY.